Method, computer program control and regulating unit for operating an internal combustion engine, as well as an internal combustion engine

ABSTRACT

In an internal combustion engine, the fuel is conveyed by an electrically driven fuel pump. The intake side of this pump is connected to a fuel tank and its outlet side is connected to a pressure region. A prerun of the electrically driven fuel pump may be performed before the startup of the internal combustion engine. In order to increase the service life of the fuel pump, an actual pressure (pactual) in the pressure region may be detected by a pressure sensor and the execution of the prerun be a function of at least the signal of the pressure sensor.

FIELD OF THE INVENTION

[0001] The present invention relates to a method of operating aninternal combustion engine, in which the fuel is conveyed by anelectrically driven fuel pump, whose intake side is connected to a fueltank and whose outlet side is connected to a pressure region, and inwhich a prerun of the electrically driven fuel pump may be performedbefore the internal combustion engine is started, an actual pressure inthe pressure region being detected by a pressure sensor and theexecution of the prerun being a function of at least the signal of thepressure sensor.

BACKGROUND INFORMATION

[0002] In a conventional method, the fuel is conveyed from a fuel tankinto a pressure region by an electrical fuel pump. A fuel injector isconnected to this region. This injector is in turn positioned in anintake manifold of the internal combustion engine. In this manner, thefuel may reach the intake manifold via the fuel injector and from therereach the combustion chambers of the internal combustion engine. Afurther method of the type initially cited is known from internalcombustion engines which operate using gasoline direct injection. Inthese internal combustion engines, the fuel is conveyed by an electricalfuel pump, which is also referred to as a “presupply pump,” from thefuel tank into a pressure region, and from there reaches a high-pressurefuel pump (“main supply pump”), which is generally mechanically driven.This pump conveys the fuel further into a common fuel line (“rail”).Multiple injectors are connected to this rail, and the fuel is stored athigh pressure therein. The injectors each inject the fuel directly intothe corresponding combustion chambers of the internal combustion engine.

[0003] If the electrical fuel pump and the pressure region positioneddownstream from it are configured as a “constant-pressure system,” thepressure region is connected via a mechanical pressure regulator to thefuel tank. In normal operation, the electrically driven fuel pumpconveys the fuel continuously and at the maximum output rate. In theknown internal combustion engines and/or the known methods, any quantityof fuel which is not sprayed into the intake manifold by the fuelinjector in systems having intake manifold injection, and which is notconveyed further by the high-pressure pump in systems having gasolinedirect injection, flows back into the fuel tank via the mechanicalpressure regulator.

[0004] Since the electrically driven fuel pump runs continuously at themaximum output rate, it is ensured that the pressure in the pressureregion always remains at the desired level, even if the maximum possiblequantity of fuel is demanded by the fuel injector and/or the injectors.

[0005] Demand-controlled fuel systems are also known. These are alsoconstant-pressure systems, in which the pressure in the pressure regionis set to a constant value through the activation of a mechanicalpressure regulator. The fuel pump is therefore no longer activatedfully, i.e., continuously at maximum output, but rather only accordingto the demand of the internal combustion engine. The excess quantity offuel flows back into the tank via a mechanical pressure regulator. Theadjustment of the conveyance output to the instantaneous operating pointof the internal combustion engine causes a savings in fuel, since thedrive output of the electrically driven fuel pump may be reduced in manyoperating ranges of the internal combustion engine.

[0006] During startup of the internal combustion engine, sufficientpressure must be provided in the pressure region of the fuel system sothat the fuel reaches the combustion chambers of the internal combustionengine in the desired manner. Typically, it is assumed that the pressureof the fuel in the pressure region falls to ambient pressure after theinternal combustion engine is shut off. In order to be able to achieve adesired pressure for starting the internal combustion engine, at leastthe quantity of fuel necessary for compressing the fuel to the desiredpressure must therefore be conveyed. The expansion of the fuel systemduring the pressure buildup must also be taken into consideration. Insome known methods, the operating time of the fuel pump, which is drivenat constant output, during the prerun is a function of the period oftime which has passed since the internal combustion engine was shut off.

[0007] Using the shutoff time of the engine, a fuel system pressure, thenumber of pump preruns which have already occurred, etc., for example,as criteria for requiring a fuel pump prerun is described in GermanPublished Patent Application No. 199 61 298.

[0008] German Published Patent Application No. 100 14 550 describes thepossibility of controlling the fuel pressure during the prerun on thebasis of a pressure sensor by changing the speed of the fuel pump.

[0009] In this method, the conveyance output of the electrically drivenfuel pump during the prerun is tailored to the particular demand. Thisdemand is defined by the signal provided by the pressure sensor. If thepressure sensor signals that the pressure in the pressure region islower than desired, the electrical fuel pump is activated accordingly.In contrast, if the pressure sensor signals that the pressure in thepressure region already corresponds to the desired pressure, theelectrical fuel pump remains switched off.

SUMMARY

[0010] It is an object of the present invention to provide a method suchthat the internal combustion engine may start even more reliably and, atthe same time, the prerun of the electrically driven fuel pump may be asshort as possible.

[0011] This object may be achieved in a method such that the electricalfuel pump is initially operated at maximum output during a prerun.

[0012] An example embodiment of the method according to the presentinvention may provide that it may be ensured that the pressure of thefuel in the pressure region necessary for an optimum start of theinternal combustion engine is reached as rapidly as possible during theprerun, and the electrical fuel pump may only be activated for theshortest possible time. This may facilitate and accelerate starting theinternal combustion engine, since the fuel pressure necessary for thispurpose is reached very rapidly.

[0013] In an example embodiment, the execution of the prerun may be afunction of whether a prerun has already been performed in the currentoperating cycle. In this manner, a prerun of the electrical fuel pumpmay be prevented from being executed after a vehicle in which theinternal combustion engine is installed is briefly switched off andstarted. This also may avoid the electrical fuel pump from being putinto operation unnecessarily.

[0014] Furthermore, a prerun of the electrical fuel pump may be executedif the actual pressure is at least equal to a specific value or lowerthan a specific value and/or the prerun may be ended if the actualpressure reaches or exceeds a specific value. This procedure may alsoshorten the operating time of the electrical fuel pump.

[0015] Alternatively or additionally, it is possible for the prerun ofthe electrical fuel pump to be ended if the duration of the prerunreaches or exceeds a specific value. This may prevent the electricalfuel pump from running too long if it is impossible to build up pressurein the fuel system (therefore, this provides a type of “safety cutoff”).In the event of cold external temperatures, the batteries which supplythe electrical fuel pump may also be prevented from being overloaded byan excessively long prerun of the electrical fuel pump.

[0016] A possibility of reaching the maximum output during the prerun ofthe electrical fuel pump which is easy to implement is for the output ofthe fuel pump to be influenced by a PI regulator as a function of thedifference between the detected pressure and a setpoint pressure in thepressure region, and by a precontroller as a function of the setpointpressure, and for the integrator of the PI regulator to be initializedas follows for a prerun of the electrical fuel pump: maximum possibleactivation output minus normal precontrol output minus activation outputof the P component of the PI regulator.

[0017] As an alternative, it is possible for the output of the fuel pumpto be influenced by a PI regulator as a function of the differencebetween the detected pressure and a setpoint pressure in the pressureregion and by a precontroller as a function of the setpoint pressureand, for a prerun of the electrical fuel pump in the precontroller, foran additional prerun precontrol output to be added to the normalprecontrol output in such a manner that the overall precontrol output isinitially at a maximum. This may be implemented using software and mayensure that the pressure in the pressure region is built up at maximumrate. However, this method may simultaneously prevent an overshootoccurring after the end of the prerun of the electrical fuel pump. Thisis a concern if the integrator of the PI regulator is initialized usinga relatively high value. Because the activation of the electrical fuelpump at maximum output is caused by the precontroller in this case, aninitialization of this type is not necessary.

[0018] In a refinement to this procedure, the additional precontroloutput may be produced by giving the value zero to the input of alow-pass filter at the beginning of the prerun of the electrical fuelpump and the low-pass filter may be initialized using the followingvalue: maximum possible activation output minus normal precontroloutput. In this case, as above, the normal precontrol output isunderstood as the precontrol output which results from the instantaneoussetpoint pressure in the pressure region of the fuel system. Such amethod may be implemented using software. Through the low-pass filter,the electrical fuel pump is initially operated at maximum output. Theadditional precontrol output is therefore initially at maximum (itcorresponds to the difference of maximum possible activation output andnormal precontrol output) and then falls to zero following anexponential function.

[0019] In this case, the time constant of the low-pass filter may be afunction of the difference between the actual pressure and the setpointpressure in the pressure region. In this case, the setpoint pressure maybe a value which is not subjected to a limitation of the maximumgradients, as is typical. If the difference between actual pressure andsetpoint pressure is very large, the additional precontrol output decaysrelatively slowly to zero. If the difference is small, the decay occursmore rapidly.

[0020] Furthermore, the setpoint pressure in the pressure region may bea function of the temperature in a region of the internal combustionengine, at least for the prerun of the electrical fuel pump. If theinternal combustion engine is warm, possibly existing vapor bubbles maybe compressed by an elevated pressure in the pressure region. If theinternal combustion engine is cold, in contrast, the prerun time may beshortened with this example embodiment.

[0021] The present invention also relates to a computer program which issuitable for performing the method above when it is executed on acomputer. In this case, the computer program may be stored in a memory,e.g., in a flash memory, a ferrite RAM, etc.

[0022] Furthermore, the present invention relates to a control and/orregulating unit for operating an internal combustion engine in which thefuel is conveyed by an electrically driven fuel pump, whose intake sideis connected to a fuel tank and whose outlet side is connected to apressure region. In order to improve the start quality of the internalcombustion engine and to reduce the exhaust gas emissions duringstarting, the control and/or regulating unit may include a memory inwhich a computer program of the type above is stored.

[0023] Furthermore, the present invention relates to an internalcombustion engine including a fuel system, which includes a fuel tank,an electrically driven fuel pump, whose intake side is connected to thefuel tank and whose outlet side is connected to a pressure region, aprerun of the electrically driven fuel pump being executable beforestarting the internal combustion engine, and a pressure sensor beingprovided which detects an actual pressure in the pressure region, andthe execution of the prerun being a function of at least the actualpressure. In order to improve the start quality of the internalcombustion engine and to reduce the exhaust gas emissions duringstarting, the internal combustion engine may include a control and/orregulating unit of the type above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a schematic illustration of an internal combustionengine including an electrical fuel pump.

[0025]FIG. 2 is a flow chart which illustrates a method of executing aprerun of the electrical fuel pump from FIG. 1.

[0026]FIG. 3 is a flow chart which illustrates a method of determiningthe activation output of the electrical fuel pump for the prerun in FIG.2, the method including a precontroller and a PI regulator.

[0027]FIG. 4 is a flow chart which illustrates a first possibility fordetermining the activation output of the electrical fuel pump for theprerun in detailed form.

[0028]FIG. 5 is a flow chart similar to FIG. 4, which illustratesanother possibility for determining the activation output of theelectrical fuel pump for the prerun.

DETAILED DESCRIPTION

[0029] In FIG. 1, an internal combustion engine is indicated as a wholeby reference number 10. It includes multiple combustion chambers, onlyone of which is illustrated in FIG. 1, using reference number 12.Combustion chamber 12 may be connected to an intake manifold 16 via anintake valve 14. A fuel injection device 18 is positioned in intakemanifold 16. A throttle valve 20 and an air mass meter 22, implementedas a hot film sensor (“HFM sensor”) are also located upstream from fuelinjection device 18 in the intake manifold. Combustion chamber 12 may beconnected to an exhaust gas pipe 26 via an outlet valve 24. A fuel-airmixture in combustion chamber 12 may be ignited by a spark plug 28. Thisspark plug is activated by an ignition system 30.

[0030] Fuel injection device 18 is part of a fuel system 32. This systemincludes a fuel tank 34, from which an electrically driven fuel pump 36conveys the fuel into a fuel line 38, which leads to fuel injectiondevice 18. Fuel line 38 is connected to an overflow valve 40 downstreamfrom electrically driven fuel pump 36. A line (without reference number)leads from this valve to an ejector pump 42, which is arranged in theregion of fuel tank 34.

[0031] The fuel pressure existing in fuel line 38 is detected by apressure sensor 44. This sensor supplies appropriate signals to acontrol and regulating unit 46, which also receives signals from HFMsensor 22 and a speed sensor 48, which picks up the speed of acrankshaft 50 of internal combustion engine 10. Furthermore, signalsfrom a temperature sensor 52, which detects the temperature of an engineblock of internal combustion engine 10, are supplied to control andregulating unit 46. A position sensor 54, which detects the position ofan ignition key 56, is also connected to control and regulating unit 46.Electrically driven fuel pump 36, overflow valve 40, ejector pump 42,and pressure sensor 44 may be implemented as one module in fuel tank 34.

[0032] On the output side, control and regulating unit 46 activates,among other things, ignition system 30, throttle valve 20, and fuelinjection device 18. Furthermore, the activation output of electricalfuel pump 36 is also set by control and regulating unit 46. This isperformed by activating a clock module 58, which outputs a pulse dutyfactor. The activation output of electrically driven fuel pump 36 isthus varied via pulse width modulation (PWM).

[0033] For starting internal combustion engine 10 (i.e., as soon as theignition is switched on), the procedure is as follows, as illustrated inFIG. 2: after a starting block 60, it is queried in a block 62 whether aprerun of electrical fuel pump 36 has already occurred in the currentoperating cycle and whether an actual pressure pactual detected bypressure sensor 44 is lower than a limit value G1. The start in block 60is initiated when a specific position of ignition key 56 is detected byposition sensor 54. The query as to whether a prerun of electrical fuelpump 36 has already occurred in the current operating cycle is performedby checking a bit B1. This check provides the result “false” if a prerunof electrical fuel pump 36 has already occurred in the current operatingcycle.

[0034] If one of the two conditions or both conditions are not fulfilledin block 62, no prerun is executed. In contrast, if both conditions arefulfilled, clock module 58 is activated in block 64 and electrical fuelpump 36 is put into operation. The activation output, whereby electricalfuel pump 36 is activated, is calculated according to a method which isdescribed in greater detail below in connection with FIGS. 3 to 5.

[0035] In block 66, bit B1 is set, indicating that a prerun ofelectrical fuel pump 36 was executed in the current operating cycle. Aslong as a prerun of the electrical fuel pump is being executed, a bit B2is set. In block 68, it is queried whether actual pressure pactual ofthe fuel in fuel line 38 is greater than or equal to a limit value G2.In the present case, both limit values are identical. However, limitvalues G1 and G2 may also be different. In addition, it is queried inblock 68 whether period tekp, which corresponds to the operating time ofelectrical fuel pump 36 during the prerun, is greater than or equal to alimit value G3. When one of the two conditions is fulfilled, the prerunof electrical fuel pump 36 is ended in block 70. In order to savecalculating time, the conditions for a prerun of the electrical fuelpump are no longer calculated when the internal combustion engine is innormal operation. This is also determined by querying an appropriatebit.

[0036] In the internal combustion engine illustrated in FIG. 1, theactivation output of electrical fuel pump 36 is determined as a functionof, among other things, actual pressure pactual and a setpoint pressurepset in a combination including a PI regulator and a precontroller. Thesetpoint value for the pressure in fuel line 38 is primarily a functionof the current operating parameters of internal combustion engine 10,e.g., of the temperature of internal combustion engine 10 detected bytemperature sensor 52, the speed of crankshaft 50 detected by speedsensor 58, the air charge detected by HFM sensor 22, and the position ofignition key 56 detected by position sensor 54. The pressure in fuelline 38 is set by an appropriate variation of the voltage (andconsequently the speed and/or the torque) of fuel pump 36. Thedetermination of the activation output of electrical fuel pump 36 isillustrated in a more general form in FIG. 3:

[0037] Subsequently, actual pressure pactual in fuel line 38 is detectedin block 74. The corresponding signal is provided by pressure sensor 44.In actual pressure detector 74, the voltage signal provided by pressuresensor 44 is averaged over ten measurement values and this averagevoltage value is converted into a raw pressure value via apressure-voltage characteristic curve of pressure sensor 44. The rawpressure value is filtered in a block 76, from which actual pressurepactual results, and this pressure value pactual is supplied to a PIregulator (block 78).

[0038] The signals of HFM sensor 22, speed sensor 48, temperature sensor52 (and possibly, for example, also position sensor 54 of ignition key56 or signals resulting therefrom) are used in a block 80 to calculate asetpoint pressure pset. This pressure is also supplied to PI regulator78. In accordance with the difference between setpoint pressure pset andactual pressure pactual, a regulator output rgl is determined in PIregulator 64, in normal operation of internal combustion engine 10. Thisoutput is produced in the form of a specific pulse duty factor, as istypical for pulse width modulation. Setpoint pressure pset and thesignals of sensors 22, 48, 52, and 54 are also used, however, in block82 for generating a precontrol output vsl.

[0039] The determination of the precontrol output for a prerun ofelectrical fuel pump 36 may occur in various manners. The goal is toprovide a desired pressure in fuel line 38 as rapidly as possible. Forthis purpose, electrical fuel pump 36 is to be activated using maximumoutput at least at the beginning of the prerun. A possibility forproviding this maximum activation output at the beginning of the prerunis illustrated in FIG. 4. In this case, the special requirements of theprerun of electrical fuel pump 36 are taken into consideration inprecontroller 82. Firstly, however, the determination of normalregulator output rgl and normal precontrol output vsl for the normaldynamic operation of electrical fuel pump 36 (i.e., when internalcombustion engine 10 is running) will be described with reference toFIG. 4:

[0040] A regulator output rgl for the dynamic operation of electricalfuel pump 36 is determined as follows: in PI regulator 78, difference dpbetween setpoint pressure pset and actual pressure pactual is formed in84. This difference dp is fed into a proportional regulator 86 and anintegrator 88. Proportional regulator 86 provides a proportionalcomponent dpp, and integrator 88 provides an integral component dpi.Both components dpp and dpi are added in 90 and converted into regulatoroutput rgl in block 92. In order to prevent overload of integrator 88,integral component dpi is delimited by limit values max and min, whichare provided in memories 94 and 96.

[0041] Precontrol output vsldyn for dynamic operation is determined asfollows: a fuel volumetric flow vol1 is determined from speed nmot,which is provided by speed sensor 48, a motor constant C1, which isstored in a memory 98, and relative fuel mass rk, which is provided inblock 100 by multiplication in 100. This fuel volumetric flow is thevolumetric flow which reaches combustion chamber 12 through fuelinjection device 18 during operation of internal combustion engine 10.

[0042] A second component vol2 is added to this fuel volumetric flowvol1 in 102. This volumetric flow is established in turn from acharacteristic curve 104, which is addressed using setpoint pressurepset. Fuel volumetric flow vol2 is the volumetric flow which flows fromfuel line 38 via overflow valve 40 (which may also be implemented as apressure relief valve) to ejector pump 42 and/or back into fuel tank 34.The sum of both components vol1 and vol2 provides the overall fuelvolumetric flow vol to be conveyed by electrical fuel pump 36. This sumis fed, together with setpoint pressure pset, into a characteristic map106, which outputs precontrol output vsldyn for dynamic operation ofelectrical fuel pump 36.

[0043] Now regarding the determination of activation output asl during aprerun of electrical fuel pump 36: in order to be able to initiallyactivate electrical fuel pump 36 at maximum output during a prerun ofthis pump, the difference between maximum permissible activation outputaslmax of electrical fuel pump 36 and precontrol output vsldyn fordynamic operation is formed in precontroller 82 if a prerun is to beexecuted. Maximum permissible activation output aslmax is stored in amemory 110 and is a function, for example, of clock module 58 used,which generates a pulse duty factor (the output pulse duty factor is afunction of the input pulse duty factor).

[0044] A low-pass filter 112 is initialized using the difference formedin 108. A time constant T of low-pass filter 112 is determined in 114using a characteristic curve, into which difference dp between actualpressure pactual and setpoint pressure pset is fed. Setpoint pressurepset is free in this case of a gradient delimitation, while in contrastit is gradient-delimited for the determination of fuel volumetric flowvol2 and for the use in regulator 78. The value zero is given to theinput of low-pass filter 112. The output of low-pass filter 112 providesa precontrol output vslvor for the prerun of electrical fuel pump 36. In116 this output is added to precontrol output vsldyn for the dynamicoperation of internal combustion engine 10 and results in totalprecontrol output vsl. In 118, this output is added in turn to regulatoroutput rgl and provides overall activation output asl.

[0045] Activation output asl for a prerun of electrical fuel pump 36 isdetermined as follows: since internal combustion engine 10 is not yet inoperation during the prerun of electrical fuel pump 36 and thereforecrankshaft 50 does not yet rotate, the multiplication in 100 results inthe value zero. Precontrol output vsldyn for the dynamic operation ofinternal combustion engine 10 thus results exclusively from fuelvolumetric flow vol2 and setpoint pressure pset. In the prerun ofelectrical fuel pump 36, setpoint pressure pset results from acharacteristic map as a function of speed nmot and a load rl or, as inthe present case, from the temperature of internal combustion engine 10,which is provided by temperature sensor 52.

[0046] However, precontrol output vsldyn determined in 106 for thedynamic operation of internal combustion engine 10 is relatively low. Acondition signals that a prerun is to occur and enables low-pass filter112. The condition is that if a time tnse is less than a limit valuegtvt, low-pass filter 112 is enabled. Due to the initialization oflow-pass filter 112 using the difference between precontrol outputvsldyn and maximum permissible activation output aslmax, precontroloutput vslvor for the prerun of electrical fuel pump 36 initiallycorresponds exactly to this difference. Since this difference is addedin 116 to precontrol output vsldyn for the dynamic operation, precontroloutput vsl at the beginning of the prerun of electrical fuel pump 36corresponds to maximum permissible activation output aslmax ofelectrical fuel pump 36. Electrical fuel pump 36 thus initially rotatesat maximum speed and maximum output, so that the pressure in fuel line38 is built up at maximum speed. As was explained above, time constant Tof low-pass filter 112 is formed as a function of the difference betweensetpoint pressure pset and actual pressure pactual. A large differenceresults in a comparatively large time constant T, while a smalldifference results in a correspondingly small time constant T. Thismeans that with a large difference between pset and pactual, precontroloutput vsl decays slower from the initialization value to zero than witha small difference. Since in this manner the difference between actualpressure pactual and setpoint pressure pset is to become smallerrelatively rapidly during the prerun of electrical fuel pump 36, a largeintegral component dpi does not built up in integrator 88 of PIregulator 78, so that an overshoot due to the regulator is avoided whenactual pressure pactual reaches setpoint pressure pset. In addition, anoverflow of the integrator is prevented in that the integrator isstopped by an appropriate bit when the maximum pulse duty factor isoutput, but actual pressure pactual is simultaneously less than setpointpressure pset.

[0047] A second possibility, using which activation output asl ofelectrical fuel pump 36 may be established during a prerun of electricalfuel pump 36, is illustrated in FIG. 5. Those functions which may ensurethat electrical fuel pump 36 is activated at maximum output at thebeginning of the prerun are implemented in FIG. 5 not in precontroller82, but rather in PI regulator 78. It is to be noted at this point thatthose elements, blocks, and functions which may be functionally similarto elements, blocks, and functions of FIG. 4 have identical referencenumbers and are not explained again in detail in each case.

[0048] Similarly to FIG. 4, a precontrol output vsldyn for the dynamicoperation of internal combustion engine 10 is determined in block 82.Also similarly to FIG. 4, the difference between maximum permissibleactivation output aslmax of electrical fuel pump 36 and precontroloutput vsldyn for the dynamic operation of internal combustion engine 10is formed in 108. This difference is converted in 120 into a pressurevalue, from which proportional component dpp, which was established inproportional regulator 86, is subtracted in 122. Integrator 88 isinitialized using the value resulting therefrom.

[0049] As a result, at the beginning of a prerun of electrical fuel pump36, regulator output rgl, resulting from the sum of proportionalcomponent dpp and integral component dpi in 90, i.e., 92, is equal tothe difference between maximum permissible activation output aslmax ofelectrical fuel pump 36 and precontrol output vsldyn for the dynamicoperation of internal combustion engine 10. Since regulator output rglis added in 118 to precontrol output vsldyn, an activation output aslwhich is equal to maximum permissible activation output aslmax resultsat the beginning of the prerun of electrical fuel pump 36. As thedifference between actual pressure pactual and setpoint pressure psetbecomes smaller, the regulator output then falls again, so that totalactivation output asl is also reduced.

[0050] It is to be noted that the initialization of integrator 88 asillustrated in FIG. 5 and the determination of precontrol output vslvoras illustrated in FIG. 4 is performed each time the condition “ignitionon” is detected (initialization of the engine control unit). Therefore,both steps are performed during a prerun of electrical fuel pump 36 andduring a normal start of internal combustion engine 10 without a prerun.It is also to be noted that the concept of “output” used in connectionwith FIGS. 3 through 5 may also be expressed in practice by a voltagevalue, a current value, or a pulse duty ratio.

What is claimed is:
 1. A method of operating an internal combustionengine (10), in which the fuel is delivered by an electrically drivenfuel pump (36), whose intake side is connected to a fuel tank (34) andwhose outlet side is connected to a pressure region (38), and in which aprerun of the electrically driven fuel pump (36) may take place beforestartup of the internal combustion engine (10), an actual pressure(pactual) in the pressure region (38) being detected by a pressuresensor (44) and the execution of the prerun being a function (62) of atleast the signal of the pressure sensor (44), wherein the electricalfuel pump (36) is initially operated at maximum output (aslmax) during aprerun.
 2. The method as recited in claim 1, wherein the execution ofthe prerun is a function of whether a prerun (64) has already beenexecuted (62) in the current operating cycle.
 3. The method as recitedin one of the preceding claims, wherein a prerun of the electrical fuelpump (36) is executed if the actual pressure (pactual) is at least equalto a specific value (G1) or is lower than a specific value, and/or theprerun of the electrical fuel pump (36) is ended if the actual pressure(pactual) reaches or exceeds a specific value (G2).
 4. The method asrecited in one of the preceding claims, wherein the prerun of theelectrical fuel pump (36) is ended if the duration (tekp) of the prerunreaches or exceeds a specific value (G3).
 5. The method as recited inone of the preceding claims, wherein the output of the fuel pump (36) isinfluenced by a PI regulator (78) as a function of the differencebetween actual pressure (pactual) and a setpoint pressure (pset) in thepressure region (38) and by a precontroller (82) as a function of thesetpoint pressure (pset), and, for a prerun of the electrical fuel pump(36), an integrator (88) of the PI regulator (78) is initialized usingthe following values or values corresponding thereto: maximum possibleactivation output (aslmax) minus normal precontrol output (vsldyn) minusactivation output of the P component (dpp) of the PI regulator (78). 6.The method as recited in one of the preceding claims, wherein the outputof the fuel pump (36) is influenced by a PI regulator (78) as a functionof the difference between actual pressure (pactual) and a setpointpressure (pset) in the pressure region (38) and by a precontroller (82)as a function of the setpoint pressure (pset), and, for a prerun of theelectrical fuel pump (36), an additional prerun precontrol output(vslvor) is added to the normal precontrol output (vsldyn) in theprecontroller (82) in such a way that the overall precontrol output(vsl) is initially at a maximum.
 7. The method as recited in claim 6,wherein the additional precontrol output (vslvor) is produced in that,at the beginning of the prerun of the electrical fuel pump (36), thevalue zero is given to the input of a low-pass filter (112) and thelow-pass filter (112) is initialized using the following value or acorresponding value: maximum possible activation output (aslmax) minusnormal precontrol output (vsldyn).
 8. The method as recited in claim 7,wherein a time constant (T) of the low-pass filter (112) is a functionof the difference between the actual pressure (pactual) and the setpointpressure (pset) in the pressure region (38).
 9. The method as recited inone of the preceding claims, wherein the setpoint pressure (pset) in thepressure region (38) is a function of the temperature (tmot) in a regionof the internal combustion engine (10), at least for the prerun of theelectrical fuel pump (36).
 10. A computer program, wherein it issuitable for carrying out the method according to one of the precedingclaims when it is executed on a computer.
 11. The computer program asrecited in claim 10, wherein it is stored in a memory, in particular ina flash memory or a ferrite RAM.
 12. A control and/or regulating unit(46) for operating an internal combustion engine (10), in which the fuelis delivered by an electrically driven fuel pump (36), whose intake isconnected to a fuel tank (34) and whose outlet is connected to apressure region (38), wherein it includes a memory in which a computerprogram as recited in one of claims 10 or 11 is stored.
 13. An internalcombustion engine (10) having a fuel system (32), a fuel tank (34), andan electrically driven fuel pump (36), whose intake side is connected tothe fuel tank (34) and whose outlet side is connected to a pressureregion (38), a prerun of the electrically driven fuel pump (36) beingable to be executed (64) before or during startup of the internalcombustion engine (10), a pressure sensor (44) being provided whichdetects an actual pressure (pactual) in the pressure region (38), andthe execution of the prerun being a function of at least the signal ofthe pressure sensor (44), wherein it includes a control and/orregulating unit (46) as recited in claim 12.